Conductive priming mixture



United States Fatent 2,970,041 CONDUCTIVE PRIMING MIXTURE -Thomas Q. Ciccone, Langhorne, Pa., assignor to the United States of America as'represented by the Sec The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

-This application is a continuation-in-part of my pending application entitled Conductive Priming Mixture, fil ed May 15, 1956, Serial No. 585,126, now abandoned.

This invention relates to conductive priming mixtures, and has as an object to present a conductive priming mixture which is not critical to ageing, needs no carbon to conduct electrical energy, does not use lead styp'hn ate for initiation, and therefore need not be blended under the critical conditions of the prior art mixtures.

In order to improve the rate of fire of automatic weapons, primer compositions were developed which functioned by transfer of electrical energy than mechanical energy, thus eliminating the need for bulky, sliding firing mechanisms, thereby reducing the firing delay between rounds.

A typical prior art conductive priming mixture comprises, by weight to total weight of mixture: about 40% leadstyphnate, 40% barium nitrate, .5 to 1% of some form of the carbon element such as carbon black, acetylene black or graphite, and remainder a heat carrier such as calcium silicide or antimony tri-sulfide.

1 One of the greatest difliculties experienced with the prior art mixtures lay in the electrical instability of tor which causes a primary explosive such as lead styphnate, to decompose, react with the oxidizer and heat carrier, generate. gas pressure which propels the burning particles into the propellant. Because the carbon contituents variable resistance, the decomposition of the lead styphnate is unpredictable, and functioning is unreliable.

My composition employs afuel-oxidant reaction, without the use of carbon. I believe that the mixture behaves as follows: upon passing an electric current throughthe mixture by means of conductor-oxidizer constituent-.-

. such as lead dioxide, causes the oxidizer (referredjtoas the primary oxidizer) to decompose and release oxygen.

The oxygen thus. released plus the heat from .the electrical current causes a reaction with fine grains. of metallic fuel, such as zirconium, which fuel acts as a flame initiator. The flame initiator then reacts with a. secondary oxidizer, thereby raising the temperatures so as toignite coarse fuel particles, while at the same timegencrating gas pressure which propels the burning particlesinto the propellant.

In some of'my earlier mixtures, I attempted to 'use i a large amount of finely particulatedmetallic fuel. How

ever, the pre ence of a large amount of the fine parti cles imparted to the mixture a plastic state unadaptable to prevailing loading techniques; dissipated electrical energy-causing misfire, and failing to have the) persistency o-ffire and particle mass suflicient to produce the action. time required of a primer.

My present mixture has none of the aforementioned disadvantages. A partial key to the solution was found to reside in particle size; Coarse grained zirconium by itself was diflicult to ignite'and had a tendency tosep arate out of the mixture: However, by reacting fine grain zirconium with a primary oxidizer to create sufficient. heat'to bring about the reaction between the secondary oxidizer and the-coarser grained fuel, the mixture produces a highly satisfactory output, as will be shown carbon, and the effect of ageing upon it. The phenom- V the functioning of the primer depended upon the molec ular-decomposition of the lead styphnatebrought about by" the heat from the carbon v-ariation in resistance of the carbon constituent correspondingly varied the decomposition of the lead styphnate, and hence primer functioning. The very presence of lead styphnate requires extreme care in handling during blending and charging, such that special loading and handling techniques need be employed.

' I have invented a conductive priming mixture which eliminates the forging disadvantages. It is not sensitive toageing after blending; does not involve the hazard associated with the handling of lead styphnate; has high uniformity of functioning; and has greater thermal output than prior art conductive priming mixtures.

v More specifically, my invention employs a fuel-oxidant' reactions rather than the use of a primary explosive.

In the typical prior art mixture, the prevailing theory i'slthat the electrical current creates heat in the conducbelow.

The method f. op r ti n isb v to eas .fo11 qws an electric current is passed into the mixture by means of the moderate conductor PbO causing a heating effect and. a release .of. oxygen which-then causes a reaction product ignites the coarse fuel particles.

t ion with fine grained zirconium, as a flame initiator, which is highly exothermic, bringing about the decomposition of 'a secondary oxidizer, Ba(NO which reac- The gas generated'during the reactions resultsin apressure which propels the burning particles into the propellant. If: isd'esiredto further improve the igniting characteristics of the mixture, a small amount of a high explosive fuel such as pentaerithritol tetranitrate (PETN) 'is' added to increase the propulsive force 'of the burning 'particles'dnto the propellant.

The general formulationcomprises: lead dioxide, as a primary oxidizer and moderating conductor, about 25 I p rts 'by weight; zirconium powder having a particle size not larger than 5 microns, as a flame initiator; about 7% parts by weight; coarsely particulate zirconium in a range 'and distribution of particle sizes such that all particles p ss through 100 mesh; about 50 weight percent pass through 200 mesh, not more than 35 weight percent pass through 325 mesh, and minimum particle size is at least 10 microns, as a fuel, about 32 /2 parts by weight: and barium nitrate as a secondary oxidizer, 35 p-"rts by weight. a

The composition has further improved characteristics 7 by the addition of pentaerithritol tetranitrate, to yield the following components and quantities: lead dioxide; 18 to 22 parts by weight; zirconium powder havinga particle'size notlarger than 5 microns, 6 to 9 parts by weight; coarsely particulate zirconium in a rangefand distribution of particle sizes such that all particles pass through 100 mesh, about 50 weight percent pass through 200 mesh, not more than 35 weight percent pass through.

325 mesh, and minimum particle size is at least 10 miflame initiator, about 7% parts by weight; coarsely particulate zirconium in a range and distribution of particle sizes such that'all particles'pass through 100 mesh, about 50 weight percent pass through 200 mesh, not more than 35 weight percent pass through 325 mesh, and minimum particle size is at least 10 microns, as a fuel, about 32 /5: parts by weight; barium nitrate as a secondary oxidizer,

. about 20 parts by weight; and pentaerithritol tetranitrate,

as apropulsive agent, about 20 parts by weight.

The advantages including safety and increased output deriving from the improved formulation are demonstrated quantitatively in the following tabulations which compare with the prior preferred mixture the properties of conductivity before and after loading, responsiveness and reliability, sensitivity to stray electrical energy and performance at extreme temperatures: 1

Effect on resistance of batch ageing Comparative resistance of loaded mixture (ohms) Improved Mixture Prior Preferred Mixture Avg. Max. Min. Avg. Max. Min.

Test No.: l

Responsiveness and reliability in terms of voltage Improved Mixture Prior Preferred ixture 2 raid 4 mid. IOmfd. 2 mid 4 mid. lomfd.

Mean Voltage v.... 26. 5 2a. 2 1s. 4 31. 35. z 30. Error of M can 0. 599 0.585 0. 535 0. 155 0. 152 0. 153 95% Confidence... 25. 3 22.0 17. 3 35. 33. 7 29. 2 Interval of Mean... 27. 7 24. 4 l9. 5 38. 6 36. 7 31. 5

Standard Devia- V 5 58. 2 53. 3 43. 9 90.0 85. 7 80. 2 All-Fire Voltage,

Corrected for skewness; 68. 9 55. 7 47. 7 96. 4 90. 0 82. 7

Statistically determined voltage at which the probability otmisfires does not. exceed 3 in 10,000,000.

Comparative safety-sensitivity to electrostatic; charge upon human'body Improved Prior Preferred Mixture Mixture 400 1'00 400 mmf. mmf. mmt". mmL.

None-Fire. Voltage I 9, 000 1,300 1,000 i 100 All-Fire Voltage Beyond 5,000 3,300 700.

ea c. r

Comparative ballistic performance Improved Mixture Prior Preferred Mixture Temperature 7 I v.* P. 'r.* v. P. T.

60.0 3.25 3,496 '59.s 3.so. 55.3 3.27 3.480 55.5--- 3.74. 16. 5 3.61 3. 296 Below Consistently Scale. Audible Hangfircs.'

*V=vcl. of projectile in foot seconds; P= ressure, p.s.i. in thousands; T=aetion time in milliseconds, measure as time. interval between application of energy to primer and emergence from muzzle of pro ectile.

' 1 It is believed that the combination as a whole, and the discovery of the approximate proportions of various materials named, especially the useof zirconium in the named particle sizes, are the factors which contribute tothe improved performance of my mixture. I I

It isfelt thatany'suitable fuel of comparably highi exothermic qualities of'about the same particle size as disclosed, could be substituted for zirconium such as. titanium, anodized magnesium, aluminum alloy'and silicone, and any suitablehigh explosive fuel could be substituted for pentaerithritol tetranitrate such as. powdered TNT, as the propulsive agent withoutdeviating from the scope of this invention.

I claim:

1. A conductive ammunition priming mixture consisting essentially of: About 25 parts by weight lead dioxide as a primary oxidizer and moderating conductor; about 7 /5 parts by weight zirconium powder having a particle size not larger than 5 microns, as a flame initiator; about 32 /2 parts by weight coarsely particulate zirconium in a range and distribution of particle sizes such that all particles pass through 100 mesh about 50 weight percent pass through 200 mesh, not more than 35 weight percent pass through 325 mesh, and minimum particle size is at least 10 microns, as a fuel; and about 35 parts by weight barium nitrate as a. secondary oxidizer.

2. A conductive ammunition priming mixture consisting essentially of about 20 parts by weight lead dioxide, as a primary oxidizer and moderating conductor; about 7 parts by weight zirconium powder having a particle size not larger than 5 microns, as a flame initiator; about 32 /2 parts by weight coarsely particulate zirconium in a range and distribution of particle sizes such that all particles pass through 100 mesh, about 50 weight percent pass through 200 mesh, not more than 35 weight percent pass through 325 mesh, and minimum particle size is at least 10 microns, as a fuel; about 20 parts by Weight barium nitrate as a secondary oxidizer; and pentaerithritol tetranitrate, as a propulsive agent, about 20 parts by weight.

3. A conductive ammunition priming mixture consisting essentially of: 18 to 22 parts by weight lead dioxide;

6 to 9 parts by weight zirconium powder having a particle size not to exceed 5 microns; 30 to 35 parts by weight coarsely particulate zirconium in a range and distribution of particle sizes such that: all particles pass through 100 mesh, approximately 50. weight percent pass through 200 mesh, not more than 35 weight percent pass through 325 mesh, and minimum particle size is at least 10 microns;

to parts by weight Biium fiitrate; and 15 to 23 parts by weight pentaerithritol tetran itrate.

References Cited in the file (if this patmt UNITED STATES PATENTS Chambers Mar. 31 1936 6 Wales "1..-; July 23, 19,46 Kurland ct a1 Mar. 20, 1951 Kenney Mar. 18, 1952 Silverstein July 14, 1953 Donnard May 19, 1959 

1. A CONDUCTIVE AMMUNITION PRIMING MIXTURE CONSISTING ESSENTIALLY OF: ABOUT 25 PARTS BY WEIGHT LEAD DIOXIDE AS A PRIMARY OXIDIZER AND MODERATING CONDUCTOR, ABOUT 71/2 PARTS BY WEIGHT ZIRCONIUM POWDER HAVING A PARTICLE SIZE NOT LARGER THAN 5 MICORONS, AS A FLAME INITIATOR; ABOUT 321/2 PARTS BY WEIGHT COARSELY PARTICULATE ZIRCONIUM IS A RANGE AND DISTRIBUTION OF PARTICLE SIZES SUCH THAT ALL PARTICLES PASS THROUGH 100 MESH ABOUT 50 WEIGHT PERCENT PASS THROUGH 200 MESH, NOT MORE THAN 35 WEIGHT PERCENT PASS THROUGH 325 MESH, AND MINIMUM PARTICLE SIZE IS AT LEAST 10 MICRONS, AS A FUEL, AND ABOUT 35 PARTS BY WEIGHT BARIUM NITRATE AS A SECONDARY OXIDIZER. 